Transmission of data with tolerable error rate in a communication network is desired. Generally, a communication system has the following components: a transmitter, a communication channel, a communication protocol, and a receiver. In most circumstances, each of these components is subject to independent design and testing specifications developed by multiple controlling organizations focusing narrowly on one element of the communication system. Also, manufacturers specializing in a particular component of the communication channel build the parts of a communication system. Thus, each of the components are typically designed, manufactured and tested independently of the other components in the system. Even if each of these components corresponds to its design and testing specifications, a communication channel assembled using the component might not perform adequately in terms of data throughput due to untested interactions among the components. In fact, most communications systems do not have any specifications and methods to test the entire system with all the actual components in place.
The International Standards Organization (ISO) has defined a layered model approach for communication networks, namely, the seven-layer model for open systems interconnection. The seven layers include the application, presentation, session, transport, network, data link, and physical layers. Each layer defines a different set of protocols necessary for communication, ranging from connectors and wires in the physical layer to identification of the reply address in an email in the application layer. Information always flows down through the layers from an application layer across a real physical connection between two or more physical layer objects.
In the highest layers (application oriented) and the lowest layers (physical or network hardware dependent) of the model, many standards are supported. However, the model is dependent on using essentially a single transport layer protocol to get all the different applications working with the different low-level networks.
Different protocols for the physical layer, for example 10BaseT or 100BaseT, can be used for data transmission. 10BaseT is a protocol that operates at 10 megabits per second (MBPS) and uses twisted-pair cabling. 100BaseT is a protocol for sending data over copper cables at a rate of 100 MBPS. Various standards govern a 100BaseT system that are different than those that apply to a 10BaseT system. The 100BaseT protocol is defined by IEEE Std 803.3u(1995), xe2x80x9cCarrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Methods-Type 100Base-T.xe2x80x9d The main components of a 100BaseT system include data source coding, framing and sharing of the cable as specified in IEEE Std 802.3u. The coding and electrical specifications of the transmitted signal and the transmitter are specified in ANSI X3.263(1995), xe2x80x9cFiber Distributed Data Interface (FDDI)xe2x80x94Twisted Pair Physical Layer Medium Dependent (TP-PMD).xe2x80x9d The specifications of the cable (for example, maximum length, impedance levels, attenuation and cross-talk) are specified by the standards TIA/EIA-568-A and TIA/EIA TSB 67. These specifications also describe connectors and patch cables. The receiver electrical and decoding specifications are described in ANSI X3.263(1995), xe2x80x9cFiber Distributed Data Interface (FDDI)xe2x80x94Twisted Pair Physical Layer Medium Dependent (TP-PMD).xe2x80x9d
Like other communication systems, a 100BaseT computer network system includes a transmitter, a receiver and a communication channel system that includes cables and connectors to interconnect the transmitter and the receiver. Even if the system components of a 100BaseT system meet their individual acceptance criteria, cable plant assembled using these components can produce unacceptable levels of data errors measured as the ratio of packets (frames) lost due to Cyclic Redundancy Check (CRC) errors or missed detection to the total packets transmitted.
Existing testing methods may test the cable and cable components. The cable, connectors and patch cables are typically tested individually by the manufacturer according to the specifications in the TIA/EIA specifications. Further, the cable plant can be tested during installation, when Cable installers verify that the installed cable and components meet the TIA/EIA specifications for an installed cable channel. Most of the testing is done using handheld meters with measuring devices attached to both ends of the cable, and is performed before the transmitter and receiver are attached to the channel.
The Network Interface Card (NIC) manufacturers test against the FDDI-TP-PMD specifications. In addition, in certain communication networks, bit error rate testers send a preprogrammed signal through the cable and test for bit errors. However, the bit error rate testers test only the cable and do not test the actual transmitter, cable and receiver combination.
However, the end user of a communication system is more interested in the overall throughput of the system than in the performance specification of the individual components. Performance information becomes more useful if a certain throughput can be guaranteed by a communication system vendor; if the guaranteed throughput can be verified after the installation; or if the system throughput can be continuously monitored over the life of the communication system.
Using a specified communication throughput as a requirement also helps the communication system component manufacturers design and improve their products to achieve a better information throughput rate. For example, a cable manufacturer can design and optimize its cable for a particular communication protocol, transmitters and receivers. Likewise, a communication protocol designer can design a protocol that works best for existing components.
Bit error rate (BER) and packet or frame error rate are both measurements of system throughput. Frame error rate includes the ratio of packets of user information received without errors to the packets of user information sent. Bit error rate includes the ratio of quantum units (example: bits) of user or system information received without errors to the quantum units of user or system information sent.
Systems do exist today that are able to measure transmitter parameters, channel parameters, and noise levels. However, no system exists that combines the readily measurable parameters to produce a predicted or actual throughput measurement. Instead, existing systems are only capable of performing empirical throughput measurements. In such systems, a signal received by the receiver contains error-detecting information. Start and end codes and cyclic redundancy codes are incorporated within the data streams. Some Network Interface Cards (NICs) are capable of detecting errors using these self-consistency checks. By counting the number of errors received against a number of bits received, a bit error rate or packet error rate may be empirically calculated.
However, Empirical measurements of BER using a physical receiver are impractical for many reasons. First, typical error rates occur on the order of one error in 1012 transmitted bits. At maximum transmission rate on a 100BaseT network, this is approximately one error in 2.8 hours. To empirically obtain a meaningful and statistically accurate error rate from a real system, one would need to measure for a duration of ten to one hundred times the error interval, so testing would require anywhere from one to ten days of measurement. Second, the physical hardware being tested is affected by a variety of external factors that cause inconsistent empirical measurements over repeated trials. This makes the calculation of an absolute BER of a communication channel (not including the receiver) impossible. Third, many physical receivers (i.e. NICs) provide only frame/packet error information. Any calculation of BER from the frame/packet error information is therefore approximate, since a packet error can correspond to more than one bit error. Finally, in many communication systems, idle signals are transmitted between packets and any system calculating frame packet errors will not identify any errors in the idle sequence between packets. Errors in idle sequence will result in loss of synchronization, and further prevent accurate measurement of BER.
The system and methodology of the present invention relate to determining the error rate and parameter margin analysis in an installed communication network. A computer network includes a transmitter, a receiver, and a communication channel system interconnecting the transmitter and receiver. The communication channel system may include, but is not limited to, patch cables and horizontal cables and the connectors at the end of cables, wall panels to which the connectors interface and patch panels that connect the patch cables to the horizontal cables.
In a particular embodiment of modeling a transmitter, the present invention captures signals from an installed transmitter, determines the transmitter parameters, replicates the transmitter pulse waveform and provides it to an arbitrary waveform generator (AWG). The AWG may then be substituted in the communication system for the actual transmitter. Further, a model is then developed that modifies the replicated pulse waveform by adjusting only physical parameters of the transmitter. In this way, the existing system may be tested for performance or parametric margins of operation, thereby identifying boundaries for successful data transmission along the communication network. Thus, in a preferred embodiment, the transmitter can be a physical transmitter, or a transmitter model built to confer certain transmitter properties, or a transmitter model which is identical to a physical transmitter with properties that can be changed individually or in combination. In an alternative embodiment of modeling the transmitter, pre-stored transmitter shapes are used with a signal generator to drive the physical cable. In another embodiment of modeling the transmitter, the measured transmitter parameters for the cable and receiver parameters are used in combination with a look-up table of headroom/error rates to predict the performance of the network.
Similarly, in a preferred embodiment, the communication channel system can be a physical medium or alternatively, a model built to comply with certain medium properties, or a medium model that is identical to a physical communication channel having properties that can be changed individually or in combination.
Further, in a preferred embodiment, the receiver can be a physical receiver, or alternatively, a model of a receiver built to meet certain receiver properties, or a receiver that is identical to a physical receiver having properties that can be changed individually or in combination.
Moreover, after characterization of the network by measurement of various operational parameters, all or part of the entire network may be virtually modeled mathematically. Once the model is developed, it is possible to vary the operational parameters and test the model for performance against the physical network in order to validate the model. Similarly, once the mathematical model is created that models the communication network, other components may be substituted for the existing components to test the network performance with different equipment. Thus, the communication network may include a physical portion and a virtual portion.
The present invention further includes the ability to vary parameters individually or in combination. In addition, the data content that is transmitted can be controlled. For example, the data content can be modeled to simulate data patterns in a real communication network. Alternatively, specific data patterns that test the response of a channel to different situations, (for example, baseline wander) can be transmitted. Further, real data captured from a physical channel can also be used as the data content transmitted.
Additionally, the present invention includes determining performance parameters after stressing the communication channel system by adjusting external parameters such as, for example, thermal, and noise parameters and electromagnetic interference sources.
Moreover, the present invention includes a method for determining a bit error rate in a computer network system. The disclosed method includes determining at least one characteristic parameter of the communication channel system, determining at least one characteristic parameter of the transmitter and determining at least one parameter of the receiver.
In a preferred embodiment, the method for determining a bit error rate in a computer network system includes sampling electrical signals in the communication channel system, measuring a plurality of cable characteristics after injecting and receiving a plurality of test signals into the computer network, and determining the bit error rate of the computer network by analyzing the measured communication channel characteristics.
Thus, the present invention relates to systems and methods to determine error rate or the throughput in a computer network. The error rate determination includes, but is not limited to, bit error rate and packet error rate in the computer network. The present invention also can provide a margin analysis for the system or components of the computer network at which the bit error rate of a specific level starts to occur.
Moreover, the present invention allows testing of all the system components together. The present invention has the ability to build and test an entire network system by using mathematical models for all the components of the system, physical components for all the components of the system, or any combination of mathematical or physical components that form the system. The mathematical models for the transmitter, the receiver, and the communication channel system can be built either from design parameters used for the design of the components or measured parameters from the existing physical components.
The present invention is versatile, as it has the ability to use values from any source, Time-Domain Reflectometry (TDR), network analyzers, parameters from handheld testers, manufacturers specification values, and user defined values.
The systems and methods of the present invention can be used by communication channel system (cables, connectors, etc.) manufacturers to design their communication channel product. The systems and methods of the present invention provide communication channel models that can determine the efficiency of their systems without the more costly alternative to building cabling systems and then testing their efficiency. Further, utility of the systems and methods of the present invention are found in the service industry where actual measurements of the communication channel systems can be performed to determine the error rate and thus, the throughput efficiency of the system. The cable plant may also be rated on its ability to perform with various types of transmitter shapes.